This application is submitted in response to Program Announcement PA-05-033, "Men's Heterosexual Behavior and HIV Infection." The broad, long-term objective is to identify interventions to dissuade South African men from engaging in behaviors that increase their risk for sexually transmitted diseases (STDs), including HIV. The Specific Aims are to (a) test the efficacy of an HIV/STD risk reduction intervention in increasing consistent condom use, (b) examine community-level and individual-level variables that may moderate the efficacy of the intervention, and (c) identify mediators that account for the intervention's effects on consistent condom use. The design of the study is a cluster randomized controlled trial. We will stratify Black neighborhoods near East London, South Africa on key characteristics and match them in pairs. We will randomly select 12 matched-pairs and within each pair, randomly assign the neighborhoods to one of two small-group interventions led by a male facilitator: a 6-hour HIV/STD Risk-Reduction Intervention or a 6- hour health promotion intervention concerning health issues unrelated to sexual behavior that will serve as the control condition. We will enroll in the trial 60 men from each neighborhood, for a total of 1,440 participants. The approach draws on social cognitive theory, the theory of reasoned action/theory of planned behavior, and the applicant's preliminary studies with men from the study population. The primary outcome is self-reported consistent condom use in the previous 3 months collected at baseline and 6 and 12 months post-intervention via audio-computer-assisted self-interviewing (ACASI). Secondary outcomes include number of sexual partners, frequency of unprotected sexual intercourse, condom use at last intercourse, and theoretical variables hypothesized to mediate intervention effects, including intentions, beliefs, and self- efficacy. The proposed research has great public health relevance because, while about one-half the cases of HIV/AIDS worldwide are linked to sexual relations between men and women, only a few studies have tested HIV/STD risk-reduction interventions specific to men. This research will test the efficacy of such an intervention in a developing country with some of the highest rates of heterosexually transmitted HIV infection in the world. Moreover, it will contribute to scientific knowledge about the kinds of men with whom it is most efficacious and the factors that account for its efficacy.